The present invention relates to a device for chilling fresh fruit and other fresh food products and, more particularly, to an improved countertop fruit chiller utilizing a Peltier effect thermoelectric device.
Thermoelectric devices operating in accordance with the well know Peltier effect have been used as cooling/heating devices for many years. Such a thermoelectric device comprises an array of semiconductor couples connected electrically in series and thermally in parallel. The semiconductor couples are sandwiched between metalized ceramic substrates. When DC electric current is applied in series to the thermoelectric device, it acts as a heat pump with heat being absorbed on the cold side, thereby cooling it, while heat is dissipated at the other side. Reversing the current causes the direction of heat flow to be reversed. Attaching a heat sink and a cold sink to the respective hot and cold sides may enhance the efficiency of the thermoelectric device.
Peltier effect devices have long been used to provide coolers and/or heaters for keeping foods fresh or for warming foods for serving. It has also been found and is well known to use forced-air convection to aid in heat transfer. A small electric fan is typically used to circulate air past the cold sink and into and through a container for the food, while another fan moves ambient outside air across the heat sink to dissipate heat from it.
Although chillers for fresh fruit and other perishable food products are well known in the art, the market success of such devices has been limited. There appear to be a number of reasons for this lack of market success. One is the cost and heat transfer efficiency of the solid state thermoelectric modules. In addition, the need to provide circulation of cool air to attain the greatest cooling efficiency has led to complex duct systems which add substantially to the cost of the containers, typically made of molded plastic materials. A long air circulation duct system also results in heat loss and pressure drop, both of which decrease the efficiency or add to the product cost. Another issue with prior chillers is the distribution of the cool air amongst the food to be chilled. It is important to optimize the distribution pattern of the cool air and to optimize the time that the cool air remains within the food container area.
In accordance with the present invention, a chiller for fresh fruit or other perishable food products utilizes a construction which optimizes a cooling air flow and thus heat transfer efficiency with a container construction that is less expensive to manufacture and permitting the use of a relatively smaller thermoelectric module. Thermoelectric modules of increased efficiency, such as disclosed in U.S. Pat. No. 5,448,109 is particularly suitable for use in the fruit chiller of the subject invention.
In its broadest aspect, the food chiller of the present invention comprises a base housing for mounting a Peltier effect thermoelectric module sandwiched between a cold sink and an opposite heat sink. The housing also defines a duct system that includes a cool air supply duct in heat transfer communication with the cold sink, a return air duct, and a cool air circulation fan in the cooling duct system to circulate air therethrough.
A food container portion is adjacent the base housing and contains an enclosing sidewall and a removable or openable cover for retrieval of the food. The food container portion has therein a plurality of inlet and outlet holes that communicate with the duct system. The inlet and outlet holes are designed to optimize the air flow.
In one embodiment these holes are oriented such that the cold airflow is induced into a circular swirling pattern. The swirling movement of the airflow helps maximize the time that cold air is in contact with the enclosed food thus improving the cooling efficiency.
In another embodiment, the cold air openings are oriented to direct the airflow away from the return air duct thus increasing the length of time the air is circulated within the food container area. The design is not restricted to these configurations as other airflow optimization patterns are also possible. The object of this invention is optimization of the airflow while minimizing manufacturing costs.
In one overall embodiment, the housing containing the thermoelectric device and duct system is separable from the food-containing portion. This embodiment allows for easy removal of the food container portion for cleaning, but requires a redundant wall at the interface of the housing and food container.
The top of the base may have holes that line up with holes in the bottom of the food container. To control the airflow rate into the food container, the food container may be rotated relative to the base thereby partially blocking the food container airflow holes.
In another overall embodiment, the housing containing the thermoelectric device and duct system is integrated with the food-containing portion thus requiring a single wall separating the two compartments. This approach minimizes manufacturing costs by minimizing the required number of components.
The food container portion is normally closed with a removable or openable cover such that cooling air is continuously recirculated. In one embodiment, however, an outside ambient air supply conduit communicates with the cooling duct system and includes a metering device to admit a controlled flow of outside air to assist in purging the cooling duct system of ethylene gas and other ripening by-products of fruit. The metering device may comprise a small diameter tube connected to the duct system upstream of the fan.
In another overall embodiment the housing containing the thermoelectric device also contains a tower comprising a portion of the duct system. Inlet air holes in the top of the tower help assure that the recirculated cold air flows to the top of the food container. To maintain a short duct length, the air out-flow holes are located near the base of the tower. The air out-flow holes are oriented such that the out-flowing air is directed toward the periphery of the food container.
To help maintain the interior temperature of the container, a removable insulating sleeve may be inserted into the container. The sleeve is shaped to conform to the interior of the enclosing sidewall. The removable cover may also be provided with an insulating liner.
Various arrangements of partitions may be placed within the container to divide the container into different temperature zones by varying the flow of cooling air through the zones. Such partitions may be vertically disposed to extend upwardly from the container bottom wall or may be horizontally disposed and attached, for example, to a central tower or to the container sidewall.